The responses of retinal rods of the turtle to annular illumination include a depolarizing component not seen when the center of the receptive field is also illuminated. While the latter feature indicates that the depolarization is of synaptic origin, it seems to exclude horizontal cell feedback as its source. Since the surround effect on rods can be seen under illumination bright enough to completely desensitize them, it must originate in the cone system and may reflect direct cone-rod interactions.